In recent years, attention has been drawn to ultraviolet curing type inks as inks used in ink jet printers and the like.
The point at which the ultraviolet curing type inks are different from ordinary water-based and oil-based inks is that the ultraviolet curing type inks are quickly cured when adhered onto recording media (for example, print paper and the like), and then, irradiated with a proper amount of a ultraviolet ray, thereby being able to maintain stable printing quality, without depending on physical properties of the recording media such as ink permeability.
In the ink jet printer using such an ultraviolet curing type ink, it is necessary to provide an ultraviolet irradiating apparatus for irradiating an ultraviolet ray on an ink adhered onto the recording medium, on the periphery of a recording head for ejecting the ultraviolet curing type ink as fine-particle ink droplets to adhere them onto the recording medium.
In the conventional ultraviolet irradiating apparatus, there has been variously proposed one in which an ultraviolet lamp such as a mercury lamp or a metal halide lamp is employed as a light source for emitting an ultraviolet ray (for example, see Patent Document 1).
However, light emitted from the ultraviolet lamp has a continuous spectrum over a wide wavelength region and includes visible light and infrared light in addition to a plurality of ultraviolet lights having different wavelength regions, so that there has been a problem that the infrared light in the continuous spectrum gives a thermal damage to the recording medium.
When a band-pass filter is provided in order to remove the hazardous infrared light, there has been a problem that the structure of a device becomes complicated, resulting in an increase in cost.
Further, the ultraviolet lamp has great power consumption, so that there has been a problem that energy saving of the ultraviolet irradiating apparatus is difficult.
In addition, the ultraviolet lamp itself is large, so that there has also been a problem that miniaturization and weight saving of the apparatus is difficult.
Consequently, associated with development of a solid laser or a light emitting diode (LED) which includes no infrared light, is capable of emitting only light of a specific wavelength region and has relatively small power consumption, there has recently been studied an ultraviolet irradiating apparatus in which these are employed as a light source, thereby preventing a thermal damage from being given to the recording medium caused by the infrared light contained, while achieving energy saving, miniaturization and weight saving (for example, see Patent Document 2).
Further, when printed images of the ultraviolet curing type inks are irradiated with these light source, there has been used a scanning system by a combination of a polygon mirror and an f-θ lens or a galvano mirror (for example, see patent document 3). However, these optical scanning systems have movable parts. This makes it difficult to further miniaturize the apparatus, and further, a decrease in reliability caused by malfunction is unavoidable.
For this reason, a light irradiating apparatus which can be further miniaturized, moreover, has no movable parts and can perform high-reliability face irradiation. As the light irradiating apparatus requiring no movable parts like this, there is considered, for example, a structure in which small-sized light sources are densely arranged.
[Patent Document 1] JP-A-2004-1326
[Patent Document 2] JP-A-2003-326691
[Patent Document 3] JP-A-2004-167793
However, there has been a problem that the structure of densely arranging small-sized light sources increases the number of light sources themselves, raises cost, and causes heat generated from the light sources to be accumulated between the light sources, also resulting in a decrease in life of the light sources due to their thermal damage and necessity of a cooling operation and means.